This little book by R.H.C. Davis was first published in 1976 and has since become a reference. Its purpose was to address a number of puzzles and issues that Norman sources, followed by a number of more modern historians, have created.
One of these is the claim that the "Norman Achievement" (to paraphrase the title of another book) illustrated some kind of superiority that they may have had on other ethnic groups between the 10th and the 12th century. The conquest of most of Normandy from their initial base (the county of Rouen), of South Italy, of England, of Wales and Ireland, and the role they played in both Spain and the Holy Land during the First Crusade tend to suggest that they had some kind of military or moral superiority - their military valor.
As Davis was one of the first to show in this book, this is exactly what the Normans wanted others to believe. It also appears quite clearly as one of the themes in the sources that are favourable to them. The first implication that this raised is the need to assess to what extent the views of the previous generations of historians (Haskins or Douglas) may have been influenced by Norman propaganda. The second consequence was the need to consider what it really meant to be "Norman", to assess whether there was a "Norman identity", how did it evolve, and what happened to it.
All of these themes are contained within Davis' small book and it has opened up new avenues of research for historians specialized in Norman history, whether French or English. It is largely because this book is so "seminal" that it remains of interest, with the author claiming that the concept of "Norman" was at his highest during the 12th century, as it was becoming weakened, but that it had disappeared by the beginning of the 13th century, especially after Normandy had been cut off from the Kingdom of England and the Kingdom of Sicily had been taken over by the Hohenstaufen family.
A worthwhile reference, in particular for those with a special interest in the Normans...